In chromaffin cells of adrenal, the sequence of molecular events whereby trans-synaptic mechanisms regulate the genetic code expression includes an increase in the cAMP/cGMP concentration ratio, an activation of cAMP-dependent protein kinase (PK) in cytosol and the translocation of the low molecular weight catalytic subunit of this protein kinase from the cytosol to the subcellular particles. The PK of nuclei is not regulated by cAMP but it increases during the trans-synaptic induction of tyrosine-3-monooxygenase (TH) because the PK catalytic subunits translocate from cytosol to the nucleus. Thus, the activation and translocation of PK, triggered by the initial increase of cAMP due to the activation of PK acts as a long range messenger for the trans-synaptic expression of the genetic code in adrenal medulla. Using primary culture of adrenal chromaffin cells, we are now trying to understand the molecular mechanisms that in chromaffin cells regulate transcription of genes after translocation of PK from cytosol to the nucleus.